This invention relates to instrumentation designed to simplify the very important and useful but relatively complex procedure of in vivo electronic examination of pacemakers (pacers).
The usefulness of this electronic examination has been well documented in the literature. Electronic cardiac pacemakers have a finite but not totally predictable lifespan. Paced patients require routine checkups to determine if the pacer is operating correctly, if the catheter leads are correct, and if the battery is running down. Routine evaluation of the pacer is prudent because it allows more accurate prediction of failure and thus may prevent wasteful early replacement as well as dangerous failure, i.e. frequent routine checks of pacemaker function are useful to optimize pacemaker longevity by allowing replacement only when necessary.
Impending failure may be heralded by slowing of the intrinsic pacer rate, change in pacer waveform duration, amplitude or shape. Failure to function correctly (inhibit, trigger) may be elicited by proper tests. Presently, complete checkups require visiting an electronic "checkup" center. That is paced patients are "followed" by specialized centers which use electronic equipment to test for pacer function, catheter integrity and battery life. Checkups occur at more frequent intervals as the pacer wears, until they may be monthly in the second or third year. The clinic visits are required because heretofore only such facilities have the assembly of equipments needed to completely test the pacer.
Electronic checks for pacer function integrity and remaining lifespan usually include recording of EKG rhythm strips to determine paced rhythm (with magnet) and spontaneous rhythm (without magnet), accurate electronic measure of pacer rate (or impulse interval), accurate electronic measure of pace (waveform) widths, and frequently a photograph (for inspection and measurement) of a high-speed oscillographic representation of the (expanded) pacer waveform.
This valuable electronic exam heretofore has required an assembly of assorted complex scientific instruments and technical equipments which should only be operated by special and experienced technicians or nurses, which assembly is large, difficult to operate, expensive to use, time consuming and are all not safely isolated, and which can require disrobing of the patient during examination. The photograph may add considerable time to the examination. The size of the equipment assembly alone requires that patients be brought to it rather then it being brought to the patient. The need to travel to the center for a checkup gives rise to a costly and burdensome task, with potential risk, for nursing home and home-bound or bedridden patients or patients living at great distances.
A typical prior art pacemaker clinic test setup is comprised of an oscilloscope with a differential input, a wide band amplifier plus a suitable "Polaroid" type camera for pacer waveform analysis, a special counter for interval and width measurement of highest accuracy and a cardiographic recorder for recording of the paced-and-spontaneous ECG. None of the above test equipments is safety isolated from ground. Photocopies of the photograph of the patient's pacer waveform are understandably of poor quality and may be blurred. As a practical matter, virtually none of the measured parameters is available and suitable for telephone transmission to, for example, a regional pacemaker clinic in case consultation is needed, or in the general situation of a remotely located patient unable for whatever reason to come to the pacemaker clinic.
As a partial or complimentary alternative to clinic checkups, there are presently available systems permitting the remote transmission of some of the required information to a clinic over the telephone, i.e. it may be considered as rather standard practice to transmit EKG and derive pacer spike interval. The usual telephone checkup consists of the patient placing a magnet over his pacer (to switch the pacer from the demand mode to the fixed rate mode), placing simple ECG leads on himself, and transmitting either his ECG and the impulse or the pacer impulse only via telephone. This is accomplished by changing the ECG into a frequency modulated tone and sending the tone into the telephone. At the center a technician uses a demodulator to reassemble the ECG and record it. An interval counter provides a more or less accurate measure of rate. The pacer waveform cannot be examined because the shape is completely lost during transmission. There is no known pacemaker follow-up telephone system that can measure and transmit the pacer pulse waveform and to provide hard copies thereof, i.e. high fidelity pictures etc. of the pacer pulse waveform in for example crystal precise time expansion of say X1000 or any other desired time base. Moreover, there is presently available no telephone arrangement capable of providing transmission of the pacer waveform, in particular for measurement and analysis of the decay time of the slope of the trailing edge of the waveform, which relates to current drain, and, therefore, battery life.
As part of an overall consideration of the shortcomings and drawbacks of the prior art, it would be highly desirable to provide an arrangement which would allow any group caring for paced patients to provide the best possible data for pacer life optimization, and such is a principle object of this invention.
It is, moreover, highly desirable to provide a portable, telephone type system capable of acquiring and transmitting from and to almost anywhere all the information usually acquired only at the checkup (i.e. on-line, real-time ECG, expanded calibration and expanded pacer waveform) of the patient at a center, by telephone for remote analysis, and such is another principle object of this invention.
It is a further object of this invention to provide instrumentation which improves the quality of care of paced patients and so simplifies the examination procedures as to make this quality care available more economically and to far greater numbers of patients, as well as enabling any EKG technican to obtain the most complete results.
It is another object of this invention to provide instrumentation which is fully capable of performing, at least, all of the measurements above-mentioned in connection with the prior art and which produces a thousand-fold time-expanded pacer waveform on an EKG recorder, all with full safety isolation.
It is yet a further object to provide a system capable of sensing, extracting, measuring, magnifying and reproducing with extreme accuracy all vital parameters of a pacemaker pulse through standard ECG leads of a patient with implanted or external transvenous pacemakers of all kinds.